The goal of this proposal is to create an ultrasensitive, chemical-specific, label-free Raman detection to enable characterization of microparticles (MPs) found in biological fluids. The particles derive from cells and are diagnostic of disease pathology, but challenge current methods of investigation. Our approach builds from initial results in our laboratory showing that we can detect individual liposomes in solution. Surface enhanced Raman scattering (SERS) from our nanostructured surface provides signal enhancements that enable particle identification. By combining microscale fluidics with nanotechnology, we will create an ultrasensitive detector that can be coupled to existing separation equipment. The specific aims of this proposal are: 1) Optimize high-efficiency SERS detection using hydrodynamic focusing in a prototype detector. 2) Demonstrate the ability to distinguish lipid vesicle samples as a model system for MPs. 3) Couple the flow detector to a capillary electrophoresis separation to analyze a complex mixture. The proposal will develop the technology, validate performance, and demonstrate utility to analyze a biological sample. We will study MPs obtained from a cell culture system to prove the efficacy of this approach. This research will produce instrumentation capable of chemical characterization at ultralow concentrations, potentially the single particle level.